Saturday, September 14, 2013

How Many Sharks Are Killed Each Year?

Guest Blog
by AJ Sablan

Ever wonder how many sharks are really killed each year globally or how these estimates are calculated?  And do you ever wonder who is behind these estimates?  It all seems very confusing and at times contradictory.

Media reports about the recent announcement by the Hong Kong government to ban shark fin soup at government functions includes this interesting little fact: More than 70 million sharks are killed every year, according to environmental group WWF.  At other times, in other outlets, the number of sharks killed annually is estimated to be 26, 38, 63, 73, 97, 100, 200, 273, or simply, tens of millions.  A myriad of organizations are credited with supplying this data, from the United Nations Food and Agriculture Organization, CITES, NOAA, WildAid, and the Pew Charitable Trusts.

There are only two peer-reviewed scientific studies that estimate the number of sharks killed each year. The first one, Global estimates of shark catches using trade records from commercial markets by Dr. Shelley Clarke et al, was published in Ecology Letters in 2006. Using trade data from the 1990s, Dr. Clarke and her coauthors estimated that between 26-73 million sharks are killed each year, with a mean of 38 million. For many years conservation organizations simplified this number by saying something like "as many as 73 million" sharks are killed each year, but Dr. Clarke prefers the more conservative 38 million.

The second study was published this year in the lead up to the Convention on the International Trade in Endangered Species of Wild Fauna and Flora. Global catches, exploitation rates, and rebuilding options for sharks by Dr. Boris Worm et al, was published in Marine Policy. The Worm study took a different approach by adding landed catch data reported to the United Nations Food and Agriculture Organization to estimates of unreported landings, finned sharks, and other discards of dead sharks. This new study suggests that between 63-273 million sharks are killed each year, with a mean of 100 million. Most shark conservation organizations have updated their materials to reflect the 100 million number as it is the more recent study and takes into account more factors than the Clarke study.

Both studies estimate the number of sharks killed, not, as  Dr. Clarke points out, “the number of sharks killed for their fins”, or “the number of sharks finned” (carcasses discarded at sea), or the “number of sharks finned alive” every year.

Determining the number of sharks finned or killed for their fins is much more difficult.  The Worm study makes an estimate on the number of sharks finned each year by calculating the number of sharks discarded in 2000 and assuming 80% were finned, which was the estimated average rate of shark finning that year.

Dr. Clarke recently used observer data to estimate how many sharks are finned in the western and central Pacific Ocean.  The results are presented in Towards an Integrated Shark Conservation and Management Measure for the Western and Central Pacific Ocean. She found that finning continues at levels of 15‐25% in the purse seine fishery and 30‐40% in the longline fishery, although the longline fishery catches over ten times as many sharks as the purse seine fishery does.  This is despite a finning ban having been in place for a number of years.

Many people confuse shark finning and shark fishing.  Shark finning is where a shark's fins are sliced off (dead or alive) and the body is dumped at sea.  Sometimes sharks are caught on a boat and brought to shore whole, with the fins sliced off on a dock or in a warehouse.  That is not shark finning.  Other times sharks are caught on a boat, the fins are sliced off at sea, and both the bodies and the fins are brought to shore.  This is not shark finning, either.  The shark finning label can only be applied to the first example.  Shark fishing can be applied to all three.

Shark finning is less of an issue than overall shark mortality.  The overfishing of sharks is threatening their populations, not the wasteful disposal of their bodies.  Even if there was full enforcement of the world's finning regulations, threatened or endangered species of shark would not be brought back from the brink of extinction because in the end, finning only determines how a shark dies, not whether it dies, or rather, lives.

The simple fact is that the number of sharks killed each year is much too high.  Sharks are slow growing, mature late, and produce few pups.  They should be managed with policies similar to those of marine mammals and turtles, not tuna and swordfish.

Alyssa Sablan is Shark Defender's student intern.  She lives in Guam.


DaShark said...

Nice post!

However the numbers you cite are those for 2000.
If you read the paper, the newer numbers for 2010 are 97 million, this within a total range of possibly 61 to 267 million.

From the same paper, finning accounts for 64% of the Sharks that were not discarded alive in 2000.
Since then, several finning bans have been enacted and enforcement is likely to be better - so the approx 40% by Clarke looks like a plausible order of magnitude.
But as you correctly remark, we simply don't know and numbers are likely to vary widely across individual fisheries.

What is clear that the overall number (approx 7% exploitation rate compared to approx 5% rebound rate) are still way too high to be sustainable

SharkBytes said...

Thank you both for the information and all you guys are doing to help sharks!

Anonymous said...

Nice blog from a pretty blogger. Very informative.

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